Fin O'Flaherty

Influence of elastic modulus on stress redistribution and cracking in repair patches

The paper presents the results of a field investigation of repairs to two highway bridges. The repairs were applied by spraying onto unpropped compression members of the bridges. Two categories of commercial repair materials were used, low stiffness materials relative to the substrate (Erm Esub). The repair materials also represented a range of other properties such as strength, density, shrinkage, and creep. The results show that repairs applied with relatively stiff materials, Erm > Esub, display efficient structural interaction with the structure. High stiffness repairs are effective in redistributing shrinkage strain to the substrate and attracting external loading in the long term. Low stiffness repair materials (Erm < Esub) are much more likely to undergo tensile cracking due to restrained shrinkage. Low stiffness repairs are ineffective in redistributing strain. 2000

Influence of resistivity on current and potential distribution of cathodic protection systems for steel framed masonry structures

Abstract The present paper presents the influence of resistivity on the current and potential distribution of cathodic protection (CP) systems for steel framed masonry structures. The work involves both experimental measurements and boundary element analysis and follows on from earlier experiments employing sand as a simple model for masonry encasement that has been reported elsewhere. Factors such as the size and type of masonry, moisture content and width of mortar joints will affect the resistance of the path through which the CP currents pass and thereby influence the distribution onto the steel surface. To represent such variations in resistance, it has been necessary to construct a small scale specimen replicating, as far as possible, actual applications on steel framed structures. The results from the laboratory specimen and numerical modelling are in sufficient agreement to confirm the validity of the modelling approach and allow the results to be employed for the purposes of design and development.

Near-surface mounted carbon fibre rod used for combined strengthening and cathodic protection for reinforced concrete structures

The dual function of a carbon fibre reinforced polymer (CFRP) rod working as the near-surface mounted (NSM) strengthening and impressed current cathodic protection (ICCP) anode for corroded reinforced concrete structures has been proposed and researched. In this paper, a CFRP rod was used for both flexural strengthening of pre-corroded reinforced concrete beams and in a dual functional capacity as an ICCP anode. After a period of ICCP operation at high current density, the beams were subjected to flexural testing to determine the load–deflection relationships. The potential decays of the steel met recognised ICCP standards, and the CFRP remained effective in strengthening the corroded reinforced concrete beams. The bonding at the CFRP rod anode and concrete interface was improved by using a combination of geopolymer and epoxy resin; therefore, the ultimate strength of a dual function CFRP rod with combination of bonding medium (geopolymer and epoxy) increased significantly.

Analysis of Stray Current Induced by Cathodic Protection on Steel-Framed Masonry Structures

Cathodic protection (CP) has been successfully employed to protect steel-framed masonry buildings from corrosion related damage. When a CP system is installed to protect the structural members, other metallic items which are within the fabric of the structure but are not in direct electrical continuity may suffer from stray current interactions, resulting in accelerated corrosion of the discontinuous items. Therefore, these must be considered when CP systems are designed prior to installation. This paper presents both experimental and numerical studies into the risk and extent of stray current corrosion in steel-framed masonry structures when subject to impressed current cathodic protection. The objective is to allow CP systems to be optimised so that interference is minimised without compromising the technical or cost benefits of this method of corrosion control.

Recommendations for the European prestandard for concrete repair

The paper analyses some of the proposals given in EN 1504, the European Prestandard for concrete repair with respect to specification of basic repair material properties. A total of ninety repair material characteristics are listed in the standard but this papers concentrates on the three properties considered important for efficient long term performance (elastic modulus, shrinkage and creep). Optimum limits for these properties are presented which will lead to satisfactory repair material performance upon compliance. The recommendations are based on findings from repairs to actual highway structures which were monitored over a long period of time. The results show that an efficient long term performance is assured when the elastic modulus of the repair material (Erm) is approximately 30% greater than that of the substrate concrete (Esub). Low shrinkage is desirable but higher shrinkage will not necessarily result in shrinkage cracking if the modular ratio, m (= Erm/Esub), is sufficiently high. Tensile creep helps reduce tension due to the restraint to shrinkage provided by the substrate concrete and steel reinforcement, especially in the early ages, when Erm is developing. The limits proposed for these properties are recommended for inclusion in the working version of the European Standard for concrete repair.